Fiber-reinforced polymeric resin composite materials are now widely used due to their outstanding strength to weight characteristics. These characteristics are especially important in the aircraft industry. Currently, structural components of these composite materials are joined to one another or to structural composites of the airframe employing other materials such as conventional metallic fasteners or adhesives. Conventional mechanical fasteners of metal are unsatisfactory for several reasons. They are subject to a weight penalty and susceptible to galvanic corrosion. Vibrations encountered during normal flight conditions and severe loading as experienced in storms or emergency maneuvers may result in failure of the fastener to composite structure joint. Adhesively bonded joints cannot be readily disassembled for service and maintenance.
While attempts to solve the aforestated deficiencies have been made using composite plastic fasteners, these earlier efforts have not been widely adopted due to economic or technical shortcomings.
For example, U.S. Pat. No. 3,495,494 to A. L. Scott discloses a threaded plastic member having a glass fiber reinforced thread in which a plurality of resin impregnated glass fiber reinforcing filaments are disposed in serpentine manner throughout the cross section of the thread and extending longitudinally of the axis of the threaded member. Manufacture of the threaded member requires a precision mold having a cavity complementary to that of the member to be formed.
U.S. Pat. No. 4,478,544 to Strand discloses a reinforced plastic rivet formed of carbon fibers encapsulated in an incompletely polymerized thermoset resin matrix. To use the rivet, its head portion is heated to soften the resin, the head is upset and fully polymerized. As with all rivets, this one is not threaded and it has further disadvantage of needing to be stored prior to use in a controlled low temperature environment to prevent premature setting of the resin.
It is evident from foregoing that a need remains for a threaded composite member that exhibits physical characteristics similar to modern composite materials such as those employed in aerospace applications and harsh chemical environments.